There have been some API and architectural changes since the message you have attached.

Actions which go through the extension port, should use the APIs from BSP_ExtensionPort.h . The 3V3 volt supply is activated when you connect the extension port to the MCU using BSP_ExtensionPort_Connect().

Please try the extension port APIs by deriving from the XdkExtensionPort example project as newer versions of the workbench may break old code.